In regard to various kinds of foils, for example hot embossing foils which are used for decorative purposes but also for example packaging foils and the like, there is from time to time a desire for the foil to be provided with a metal coating thereon, only in specified regions or areas thereof, for example to define a pattern on the foil so that for example lettering, pictures and other forms of graphics can be produced on the foil, which have a metal effect or appearance. When dealing with foils of the above-indicated kind, the operation of applying the metal coating to the surface thereof is usually effected by a vapour deposit operation or a similar kind of process, over the entire area of the foil. In the past therefore, for that reason, when a coating of metal is required on the foil only over a given region thereof, the mode of operation may be such that the layer of metal on the foil is suitably covered over, for example by printing over the parts of the metal layer which are not to be visible as such, so that the metal layer can be seen only in the required areas in which the metal has not been covered. When using that mode of procedure however, there is the risk that the layer which covers over the metal coating on the foil may become worn away in use of the foil, so that the underlying metal can then be seen. Another possible mode of operation is for the layer of metal, after having been applied to the foil, to be covered in the appropriate regions thereof with a lacquer which is not attacked by certain etching agents which, on the contrary, will attack the layer of metal, with the metal layer then being etched away in the regions thereof which are not covered by the etch-resistant layer, whereupon the etch-resistant layer has to be washed away in order to expose the areas of metal which still remain on the foil in the appropriate configuration. It will be appreciated that such a procedure is complicated and in some cases may also give rise to quite serious environmental pollution by virtue of using solvents which give off etching vapours and in most cases solvent vapours also.
In regard to the production of hot-process embossing foils, one mode of operation which has previously been employed provides that the carrier or backing foil which is optionally provided with a layer of protective lacquer thereon, is provided with a coating of lacquer, for example by a printing process, in the areas of the carrier or backing foil in which no coating of metal is to appear. The layer of lacquer applied to the backing foil can be dissolved away by means of a solvent that does not attack the backing foil or the above-mentioned coating of protective lacquer that is optionally applied thereto. When the lacquer has been applied to the areas on the backing foil in which no metal is to be deposited, metal is applied to the backing foil by a vapour deposit operation. Then, the layer of metal is removed again in the areas of the backing foil in which no metal coating is required thereon, by dissolving the soluble lacquer. A process of that kind enjoys more particularly the advantage that it is possible to produce extremely fine and delicate patterning effects because the operation of applying the soluble lacquer to the backing foil by a printing operation can be performed virtually as desired, to give the required effects.
However, that process suffers from the disadvantage that the surface which is to be coated with metal is generally relatively uneven, which results in metal coatings of differing thicknesses, which in turn can have disadvantageous effects on the finished product, that is to say, the article resulting after partial selective removal of the coating of metal by the step of dissolving away the soluble layer. However, the above-indicated process also suffers from the particular advantage that it is virtually impossible to produce colour effects in regard to the metal layer. In order to produce the impression of a coloured metal coating, it is necessary for the layer of metal to be covered on the visible side thereof with a transparent, coloured coating of lacquer. If now that transparent, coloured coating of lacquer is applied between the soluble lacquer and the backing foil, it is not also removed together with the portions of the metal coating which are to be removed, so that it is not just the metal coating but also the background areas that are correspondingly coloured, and that is unacceptable in many cases. In such situations, it would then be necessary for the transparently coloured layer of lacquer to be applied only after the soluble coating of lacquer has been formed. In that case however, serious complications arise in the operation of dissolving away the soluble lacquer because, before the solvent can act on the soluble lacquer, it first has to penetrate through the coating of transparent lacquer. The only remaining possibility finally in regard to the known process is for the coating of metal to be coloured by staining by means of a highly viscous agent. As however such an agent would have to be applied before the coating of metal is formed on the backing foil or a coating of cover lacquer where provided, there is the risk that the staining effect on the coating of metal that is subsequently produced is not very strong, and in particular it is only possible to produce a really weak colouration effect.